In a vehicle with electric power steering, the steering boost torque is provided by an electric motor coupled to the steering column. An example of such a system is described in U.S. patent application Ser. No. 08/538,155, Electric Power Steering Control, filed Oct. 2, 1995 and assigned to the assignee of this application. FIG. 2 of this application shows a controller 16 which derives an assist torque signal and a return to center or neutral position torque signal and sums these torque signals to produce a motor command signal. The first of these torque signals provides the power steering boost torque, and the latter provides return to center bias torque. However, the system has a free rotational oscillation resonance of about 2 Hertz which may not be satisfactorily damped by the apparatus shown. In order to provide a crisp, controlled feel to the steering, it may be advisable to provide active damping.
Alternatively, some vehicles may provide a return to center torque through the characteristics of their suspension systems without the need for such a torque to be provided by an electric power steering system itself. However, such vehicles may provide an overshoot in the return to center torque which makes active damping desirable.